Low Carbohydrate, High Protein (Ketogenic) Diets for Weight Loss

Article by James Collier BSc (Hons) - Moderator and Contributor to Muscletalk as an Expert in Nutrition

There has been a few posts regarding low carbohydrate, high protein or ketogenic diets on MuscleTalk, so I thought I'd voice my views through an article. I am referring to them in the non-bodybuilding sense here, and more for body weight loss. Ketogenesis may be useful if used appropriately in the last part of bodybuilding contest preparation, but the reasoning behind this is very different to general weight loss.

Collectively, these regimens are known as 'low carb' or 'ketogenic' diets and have many variants. One of the better known is the Atkins diet, around since the 1970s. Others include Radiant Health (Professor Brian Peskin), the Carbohydrate Addicts Diet (Dr Richard Heller and Dr Rachel Heller), the Diet Cure (Julia Ross), Protein Power (Dr Michael Eades and Dr Mar Eades), Eat Fat, Get Thin (Barry Groves), and many more.

The ClaimsThese diets claim to alter the way we metabolise food, and their advocates argue that obesity is a consequence of dietary carbohydrate rather than dietary fat or total calories. It is claimed that excess dietary carbohydrate raises insulin levels which, in turn, causes more body fat deposition. The theory is that a higher protein in relation to carbohydrate intake lowers insulin levels and causes weight loss. These diets are also said to help food cravings and help fill you up as protein foods promote satiety. Other health claims are that they improve lipid profiles and benefit hypertension.

The Scientific EvidenceThere is absolutely no evidence, though, that weight loss can be achieved in any way, other than by creating a negative energy balance, i.e. weight is lost when we burn up more than we eat. There is also considerable evidence that some of the health parameters are closely linked to obesity, and that weight loss by any means improves them1.

There is evidence that calorie deficient low carbohydrate, high protein diets do produce a more rapid and greater initial weight loss compared to isoenergetic more moderate carbohydrate diets, with the associated benefits 2,3. Unfortunately, the initial high rate of weight loss is not only due to reduction in energy stores, but primarily due to changes in fluid balance. The reduction in muscle glycogen (the storage form of carbohydrate) stores is accompanied by a reduction in water; for every 1g glycogen metabolised, 3g of water is lost.

Also, on extremely low levels of dietary carbohydrate (i.e. less than 50-100g per day; 10-20% total energy intake) high levels of ketones are produced. Ketones are used as a fuel by the brain and heart muscle during times of low food intake and help keep us alive. The presence of ketones means increased sodium and potassium and associated water loss (more weight loss), bad breath, taste changes and nausea, which obviously may lead to reduced food intake.

Ketogenic diets are very limited in variety, and variety in the diet is one of the fundamental healthy eating guidelines in order to achieve a balanced diet and optimal nutrition. They fill you up more than on diets of comparable energy intakes with a higher carbohydrate : protein ratio. Protein rich diets also increase thermogenesis, and therefore 24-hour energy expenditure more than with similar energy higher carbohydrate intakes 4. Whether this persists longer term remains untested.

As a consequence of all the above in ketogenic diets, there is greater potential for a negative energy balance, hence consequential weight loss. Weight loss is therefore not due to raised serum insulin levels promoting body fat deposition. There is also going to be a considerable consequential reduction in muscle tissue as protein is burned for energy.

Potential ProblemsLow carbohydrate diets are, by definition, high in protein and fat. As less fibrous starches are consumed, there is a reduction in dietary fibre intake too, as well as antioxidant vitamins and minerals. These factors signify increased risk of cardiovascular diseases, cancers, kidney disease and bowel disorders.

Nutritional intakes of people on ketogenic diets have been shown to be low in calcium content, as are the intakes of people following more orthodox weight reducing regimens. This is a result of general low food intake. However, low carbohydrate, high protein diets may also lead to increased calcium excretion and reduced bone mineral content (5). It is very likely that there is an increased risk of osteoporosis later in life.

In SummaryKetogenic diets are no 'magic' answer for weight loss, and certainly do not follow the well-evidenced healthy-eating guidelines. They also have the potential to cause nutrition related problems to health.

However, there are no studies comparing the short-term use of such diets in relation to health problems, so there may well be benefits of short-term use outweighing any potential risk for certain obese people who really struggle to lose weight by more traditional means 6. There is no evidence describing what 'short term' actually means. Further research is therefore required. Also the extent of physiological adaptation to these regimens is unclear.

There is very good evidence though, that manipulation of low fat, moderate protein and moderate carbohydrate is more promising in respect of efficient and consistent weight reduction 6 This, of course, is improved further with the inclusion of exercise.

Whilst many people do claim some good initial weight loss with low carbohydrate, high protein diets, this rate of loss slows down after a few weeks. Most people also claim to put most, if not all, the weight back on (and sometimes more) when they cease the 'diet'. Therefore defeating the object of following such a stringent plan. Many may follow such regimens for a special occasion or seasonal preference, which could lead to significant weight cycling, identified in its own right as a risk factor for cardiovascular disease.

Low carbohydrate, high protein diets do not fit in with healthy eating guidelines, they are unbalanced and difficult to fit in with lifestyles and family meals. They also take no account of the psychological influences of why people over eat, crucial in any weight reduction programme.

Many MuscleTalk members will be looking to reduce body fat whilst maintaining muscle mass, but ketogenic diets are not the way to go for the reasons discussed above. Remember that most of you will be wanting to either build muscle, or, at least, to maintain muscle mass - this is not achievable with low carbohydrate, high protein diets

REFERENCES

British Nutrition Foundation (1999). Obesity. The report of the British Nutrition Foundation Task Force. Blackwell Science